As a high-speed mobile communications system which adopts a CDMA method, the telecommunications standard called the third generation and referred to as IMT-2000 is adopted by the International Telecommunications Union (ITU). Commercial services based on W-CDMA (FDD: Frequency Division Duplex) technology were started in Japan in 2001. A W-CDMA (FDD) system is a third-generation mobile communications system, and aims at acquiring a transmission rate of up to about 2 Mbps per mobile station. For W-CDMA (FDD) systems, the first specifications were determined in the 1999 released edition which the standardization organization 3GPP (3rd. Generation Partnership Project) summarized in 1999.
Currently, release 4 and release 5 are defined as other new versions of release 1999, and release 6 is being generated.
In the above-mentioned standards, it is assumed originally that a service which offers continuous data like voice data is provided. For this reason, even when carrying out burst transmission such as transmission of packets from a mobile station to a base station, a dedicated channel DCH (Dedicated CHannel) is always ensured, as a radio resource, for each mobile station. This presents a problem from the viewpoint that effective use of radio resources is needed as the use of packet data increases in recent years because of the proliferation of the Internet.
Furthermore, since transmission of data from a mobile station is carried out through autonomous transmission control (Autonomous Transmission) by the mobile station, the timing of transmission by each mobile station is arbitrary or random. Therefore, in a CDMA communications system, since transmission from other mobile stations all serves as a source of interference, a base station can only predict the amount of interference noise at a time of receiving data from each mobile station and the amount of variations in the interference noise amount statistically. Therefore, in the management of radio resources, it is necessary to suppress the throughput and the mobile station maximum transmission rate by assuming a case in which the amount of variations in the interference noise is large, and to carry out control of assignment of radio resources to ensure margins.
Actually, the radio resource management for mobile station transmission (for uplink), which is defined by the W-CDMA standard, is not carried out by a base station itself, but is carried out by a base station control apparatus (RNC: Radio Network Controller) which organizes a plurality of base stations. Hereafter, a combination of a base station and a base station control apparatus will be referred to as a base station side. It takes a relatively long process time of about several hundred msec for a base station control apparatus (RNC) to perform each of management of radio resources on a mobile station and an exchange of management information with the mobile station. For this reason, a problem with a base station control apparatus is that it cannot carry out high-speed control of assignment of radio resources while monitoring a high-speed change in the radio propagation environment, the amount of interference from other mobile stations, etc.
Nonpatent reference 1 proposes an on-demand channel assignment method for uplink as a technology for providing enhancement of uplink performance/expansion of functions on the basis of the above-mentioned current standards (releases 1999, 4 and 5).
According to FIG. 1 of nonpatent reference 1, a mobile station (UE: User Equipment) with packets to be transmitted notifies information (Queue size) about the amount of data of yet-to-be-transmitted packets and mobile station transmit power margin information (Power Margin), as a packet data transmission request, to a base station (NodeB) via a channel for transmission request (USICCH: Uplink Scheduling Information Control Channel). The base station which has received this request notifies a radio resource assignment result (or a scheduling result), such as a transmission timing, to the mobile station via a downlink assignment control channel (DSACCH: Downlink Scheduling Assignment Control Channel). The mobile station transmits packet data to the base station via a channel for data transmission (EUDCH: Enhanced Uplink Dedicated Transport Channel) according to the received scheduling result. The mobile station transmits information, including information about a modulation method at the time of the transmission of packet data to the base station, to the base station via a type-of-modulation information channel (UTCCH: Uplink TFRI Control Channel) separately. The base station judges whether it has received the packet data correctly, and notifies ACK/NACK indicating the judgment result to the mobile station via a channel for notification (DANCCH: Downlink Ack/Nack Control Channel). Although it can be assumed that these channels are an extension of conventional standard channels or new channels which are introduced into the system, the details of the channels have not been proposed yet.
Nonpatent reference 2 proposes a technology generated on the basis of nonpatent reference 1.
As conventional examples of a technology for notifying information on the amount of data to be transmitted from a mobile station to a base station, there are a packet communication method, as disclosed by patent reference 1, of a mobile station notifying the amount of data to be transmitted in response to polling from a base station, a packet transmission method, as disclosed by patent reference 2, of a mobile station notifying the size of packets to be transmitted to a base station, and the base station assigning radio resources on the basis of the packet size notified thereto, and a method, as disclosed by patent reference 3, of a base station assigning radio resources on the basis of available transmission power, the amount of transmission data, QoS, or the like notified from a mobile station.
However, patent references 1 to 3, and nonpatent references 1 and 2 do not disclose any concrete method about the format of information on transmission data at the time of transmission of the information on transmission data.
According to the conventional W-CDMA standard, when information about the amount of yet-to-be-transmitted data transmitted from a mobile station is temporarily received by a base station, the information about the amount of yet-to-be-transmitted data is notified to a base station control apparatus (RNC) juts as it is. For this reason, the base station cannot grasp the contents of the information about the amount of yet-to-be-transmitted data. Therefore, the base station cannot implement such uplink radio resource control as disclosed in patent references 1 to 3 and nonpatent references 1 and 2. Furthermore, according to the conventional W-CDMA standard, there is provided no means for notifying the information about the amount of yet-to-be-transmitted data of a mobile station from a base station control apparatus to a base station (NodeB). Even if it is possible to provide a means of temporarily sending information which the base station control apparatus has acquired to the base station, because the transmission period of the amount information of yet-to-be-transmitted data from the mobile station to the base station control apparatus is set to a long time period such as 250 ms, 500 ms, . . . , or 6,000 ms, there is a problem that the base station cannot perform high-speed radio resource control.
Nonpatent reference 3 proposes a technology about the notification timing of mobile station information, including amount-of-data information about the amount of yet-to-be-transmitted data, and a transmit power margin, which is related to the on-demand channel assignment method disclosed by nonpatent reference 1. In nonpatent reference 3, various transmission methods, such as a periodic transmission method, are shown.
However, only a proposal about the notification timing is disclosed by nonpatent reference 3, and no concrete method about the format of notification, transmit channel specification, etc. at the time of transmission of packets is disclosed by nonpatent reference 3.
Nonpatent reference 2 further discloses, as another on-demand channel assignment method, a method of reporting, as a packet data transmission request, not the above-mentioned amount of yet-to-be-transmitted packet data of the mobile station, but a transmission rate (Rate Request) which the mobile station desires to the base station via an uplink channel (Rate control scheduling). The base station carries out scheduling on the basis of the transmission transfer rate request from each mobile station in the cell, and, after that, notifies, as a scheduling result, a grant transmission transfer rate (Rate Grant) to each mobile station via a downlink channel. However, nonpatent reference 2 discloses no concrete method about the format of request, transmit channel specification, etc. at the time of transmission of packet data, like nonpatent reference 1.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a mobile station, a base station, a communications system, and a communications method which are suitable for a case in which report information from a mobile station which is needed for radio resource control for uplinks in a base station is notified from the mobile station directly to the base station at a high speed.    [Patent reference 1] JP,64-42951,A    [Patent reference 2] JP,2002-374321,A    [Patent reference 3] JP,2003-46482,A    [Nonpatent reference 1] “AH64: Reducing control channel overhead for Enhanced Uplink”, [online], Jan. 7-11, 2003, 3GPPRAN1#30, and [retrieved on Jan. 7, 2004], the Internet <URL:http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_30/Docs/Zips/R1-030067.zip>    [Nonpatent reference 2] “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Feasibility Study for Enhanced Uplink for UTRA FDD” (Release 6), [online], 2004-3, TR25.896v6.0.0, [retrieved on May 10, 2004], the Internet <URL:http://www.3gpp.org/ftp/Specs/2004-03/Rel-6/25_series/25896-600.zip>    [Nonpatent reference 3] “Uplink signaling of scheduling information”, [online], [retrieved on Jan. 7, 2004], the Internet <URL:http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_34/Docs/Zips/R1-031056.zip>